This invention relates to the alignment of liquid crystal (LC) molecules in liquid crystal devices. Although the description which follows deals with liquid crystal displays (LCDs), the primary intended application, the invention is also useful in other devices such as optical shutters.
In a conventional LC cell the interior major surfaces of the glass plates are each coated with a polymer. The polymer layers are rubbed (e.g., with a cloth) to orient the polymer chains along a predetermined direction. LC molecules contacting the polymer align themselves along the predetermined direction. Thus, the polymer layers are known in the LC art as alignment layers. In the absence of such layers, the LC molecules at the cell surface would tend to orient themselves randomly in contrast with being pinned by the boundary conditions established by the alignment layers.
Nematic LC materials, for example, can be easily aligned by coating both of the interior surfaces of the cell with a polymer (usually polyimide) and by unidirectional rubbing of both of the polymer layers. If an appropriate crystalline polymer is used, such a surface treatment can also align smectic LC materials.